Hex, Localtime and strings

theneil has asked for the wisdom of the Perl Monks concerning the following question:

Trying to print the time from a substring (time is in Hex):

Why does this work?

print MYFILE scalar(localtime(0x506143ca));
#
#Prints: Tue Sep 25 00:40:26 2012
#
[download]

But not this:

my $daTime = "0x506143ca";
print MYFILE scalar(localtime($daTime));

#
#Prints: The default date - something like Jan1 1969
#
[download]

Any help is greatly appreciated! Thanks!

Comment on Hex, Localtime and strings Select or Download Code

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Re: Hex, Localtime and strings by Fletch (Bishop) on Sep 26, 2012 at 17:18 UTC
Because the former is a numeric literal where the `0x` prefix means something; the later is a string treated as a number which presumes base10 (which means it gives up when it sees a non-digit "x" and is numerically `0`). You need to use oct to get the string value treated like it would be as a numeric literal. The cake is a lie. The cake is a lie. The cake is a lie.	[reply] [d/l] [select]
Re: Hex, Localtime and strings by davido (Cardinal) on Sep 26, 2012 at 17:18 UTC
Because the first example uses a hex representation of an integer, and the second example uses a string of characters that happen to include a 0x and some stuff that looks (to a human) hex-ish (but not to Perl). Perl converts that string to a number following Perl's numerification of a string rules, which in this case results in a '0'. `use strict; use warnings; use diagnostics; my $daTime = "0x506143ca"; print scalar localtime $daTime, "\n";` [download] ...the output... `Argument "0x506143ca" isn't numeric in localtime at mytest.pl line 10 +(#1) (W numeric) The indicated string was fed as an argument to an oper +ator that expected a numeric value instead. If you're fortunate the me +ssage will identify which operator was so unfortunate. Wed Dec 31 16:00:00 1969` [download] As for the "`Wed Dec 31 16:00:00 1969`": `perl -E 'say localtime 0'` will yield the same result. Dave	[reply] [d/l] [select]
Re^2: Hex, Localtime and strings by theneil (Novice) on Sep 26, 2012 at 17:25 UTC
Thank you guys! Worked like a charm! I'm slowly learning :)	[reply]
Re^3: Hex, Localtime and strings by simatics (Initiate) on Jun 22, 2013 at 14:25 UTC
I know this is late, but I'll share what worked for me! `$hexval = hex '51C07405'; print scalar(localtime($hexval));` [download]	[reply] [d/l]
Re: Hex, Localtime and strings by toolic (Bishop) on Sep 26, 2012 at 17:31 UTC
You can also use hex: `print scalar(localtime(hex($daTime)));` [download]	[reply] [d/l]
Re: Hex, Localtime and strings by sundialsvc4 (Abbot) on Sep 26, 2012 at 18:09 UTC
Now might also be a good time to look at, for example, Date::Calc::Object, and the many other date/time routines available on CPAN. I particularly like this one because, as the name implies, it introduces the notion of a “date/time object.” Which just turns out to be an extremely useful notion to have. A date value, regardless of how you introduced it to the system, becomes “a thing” that you can query and manipulate and “do things with” in a very natural way. Every kind of date/time manipulation can be found somewhere in CPAN ... even for archaic calendars. (It’s great fun to go poking around in there to see what you find.)	[reply]


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